Properly close session in AsyncInferenceClient

[Wauplin]

Close #2493.

This PR adds the possibility to properly close sessions from a AsyncInferenceClient object using either close or a context manager:

import asyncio

from huggingface_hub import AsyncInferenceClient

model = ...  # NOTE: I'm using a self-hosted TGI instance

async def run():
    client = AsyncInferenceClient(model)
    answer_stream = await client.text_generation(
        "Between emacs and vim, the best editor is",
        stream=True,
    )
    await client.close()

asyncio.run(run())

or a context manager:

async with AsyncInferenceClient():
    for token in await client.text_generation(
        "Between emacs and vim, the best editor is",
        stream=True,
    ):
        break  # no one wants the answer

If some sessions are still opened when a client is being deleted, a warning is emitted to the user to tell them how to properly handle things.

Thanks @tomjorquera for the very well described issue which helped a lot building this PR :)

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[LysandreJik]

Awesome, thanks @Wauplin!

[LysandreJik]

Out of curiosity, shouldn't this just close the session as well?

[Wauplin]

Well well well...

I got a hard time getting to make it work. The thing is that you don't know when __del__ is called by Python's garbage collector. Since self.close is an async function, you need an active event loop to make the close method run -which is not guaranteed. I first tried some hacks but gave up given the complexity compared to having a proper close method or using an async context manager.

This answer on stackoverflow also convinced me of doing things like this.

[Wauplin]

Thanks for the review!